Remove feature toggle va_online_scheduling_facilities_service_v2

[JunTaoLuo]

Description

This is a followup to the initial feature toggle spike ticket. This feature toggle was used during v2 migration which has long been complete. We will need to remove the feature toggle from the list and the application code.

Requirements

• Remove feature toggle va_online_scheduling_facilities_service_v2 from the flipper list and the application code.

Design Assets

N/A

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Acceptance Criteria

• vets-website: Remove this feature toggle and update any logic where it's used
• vets-api: Remove this feature toggle and update any logic where it's used
• Update the documentation
• remove the feature toggle in non-prod environments (dev, sandbox, staging)
• file platform request to remove the feature toggle in prod environment

Definition of Done

• All acceptance criteria are met